The long-range goal of this project is to determine how somatosensory information is processed by somatosensory (SI) cortex. Progress in the diagnosis and treatment of disordered functioning in the human brain in stroke and disease, particularly in chronic conditions leading to severe disorders of sensory perception, depends on an understanding of the fundamental principles of organization of SI. Sensory information is relayed from skin receptors centrally along parallel channels which carry different types of somatosensory information. The organization of these parallel channels in SI cortex is not known, but it has been assumed that convergence of information in SI underlies the ability to perceive certain aspects of complex tactile stimuli. The proposed research is designed to reveal the intrinsic physiological and anatomical organization of SI which underlies this processing. Techniques which will be used to investigate relationships between anatomical and physiological properties of single neurons in SI inlude: extracellular recordings of neuronal responses to computer-controlled tactile stimulation (from single neurons and pairs of neurons); intracellular recordings coupled with injection of horseradish peroxidase to label the recorded neurons; and immunocytochemistry to identify neuronal elements which contain GABA. The specific aims are to: (i) determine the organization of thalamic input to SI; (ii) determine the response properties of neurons in identified laminae of SI; (iii) determine the morphology of physiologically identified SI neurons; (iv) determine the relationship between identified SI neurons and other neurons which contain GABA (an inhibitory neurotransmitter which influences cortical neuron responses); and (v) determine the intrinsic physiological organization of SI by cross-correlation analyses of recordings from pairs of neurons.